Figure 2: Prevention of global leftward flow by methylcellulose.

(a) Mouse embryos at the EHF stage were transferred to culture medium containing 0, 0.5 or 1.0% (w/v) methylcellulose, and the motility of node cilia and nodal flow were monitored. Whereas node cilia generated the leftward global flow in control medium (left panel), ciliary motion and fluid flow were completely lost in medium containing 1.0% methylcellulose. In the presence of 0.5% methylcellulose, the weak leftward local flow generated by ciliary rotation was observed (right panel). The black scale bars indicate 10 μm. Red arrowheads denote local leftward directional flow. A, anterior; P, posterior. (b) Mouse embryos harbouring the Pitx2 ASE-lacZ transgene were isolated at the EHF stage, cultured in the presence of 0, 0.5, or 1.0% methylcellulose for 5 h, and then transferred to culture medium containing 1.0% methylcellulose and incubated for an extra 12 h. L–R asymmetric gene expression in the lateral plate was monitored with the Pitx2 ASE-lacZ transgene as a reporter. L, L′, Bi, R′, and R denote exclusively left-sided, left side–dominant, bilateral, right side–dominant, and exclusively right-sided expression of the transgene, respectively. The numbers of embryos showing each phenotype are presented in the coloured boxes. Representative embryos stained with the β-galactosidase substrate X-gal are also shown, with the red arrowheads indicating lacZ expression. The red scale bars indicate 1 mm. The black arrow indicates 5 μm s⁻¹.